Field of the Invention
The present invention relates to an imaging device and an imaging system.
Description of the Related Art
One type of circuit configurations of a complementary metal oxide semiconductor (CMOS) image sensor has analog-to-digital (AD) conversion circuits provided correspondingly to columns of a plurality of pixels. In relation to such a CMOS image sensor, Japanese Patent Application Laid-open No. 2010-103913 discloses that a thermal noise caused by operation of an imaging device can be reduced by performing, or applying, AD conversions for signals from pixels for multiple times and adding digital values obtained by the AD conversions.
Further, Japanese Patent Application Laid-open No. 2013-93837 discloses an imaging device in which a counter outputs a count value to a storage on each column via a buffer. This storage on each column of the imaging device holds a count value at a timing when the magnitude relationship between the potential of a pixel signal and the potential of a ramp signal is inverted.
In the configuration of Japanese Patent Application Laid-open No. 2013-93837, however, multiple AD conversions for input pixel signals requires additional storages for holding the AD conversion results for respective times, which may result in an increase of the number of elements.